AVS Forum banner
Status
Not open for further replies.
1 - 20 of 33 Posts

·
Registered
Joined
·
1,535 Posts
Discussion Starter · #1 ·
Why is the signal rate on HBO-HD so low? Is it to save sat bandwidth? Fifth Element was about 11Mb/sec (10GB for the 2H movie) and Shrek was about 9.3Mb/sec (6GB for the 1.5H movie) - that's less than some of my DVDs!


Leszek
 

·
Registered
Joined
·
13,531 Posts
leszek,


HBO HDTV uses variable bit rate (VBR). Transport stream analysis shows they they run anywhere up to ~14.2Mbps on intense scenes, and down to ~7Mbps on less intense scenes. Based on prior posts, it looks like HBO is using 24fps with repeat flags.


HBO probably set their bit rate, in part, to accomodate the bandwidth limitations of content providers (i.e. DirecTV), who wanted at least two HDTV movie channels per transponder. DirecTV is using QPSK 6/7 FEC, so it has approximately 31.5Mbps usable per transponder. Dish Network gets a little less on their QPSK transponders, about 30.7Mbps usable. Of course, Dish Network can get more with 8PSK---up to 46Mbps with 5/6 FEC.
 

·
Registered
Joined
·
1,235 Posts
Wow. I've never seen HBO-HD but that's gotta be BAD. Stuff gets pixellated easily on 19.3 mbps OTA signals. I can only imagine what 9.3 mbps might do to the picture. They've been trying to get red-laser-based HD-DVD working with advanced codecs at 7mbps, but it would never occur to someone just to use mpeg2 at that rate. Does it look as bad as it sounds like it does?
 

·
Registered
Joined
·
13,531 Posts
Quote:
Wow. I've never seen HBO-HD but that's gotta be BAD. Stuff gets pixellated easily on 19.3 mbps OTA signals.
Actually, most of the CBS 1080i film-based sources do very well in 11-12Mbps. It is the live events and sports broadcasts (with HD cameras), that need significantly more than that.


If one were to have recorded the Mike Tyson fight on Showtime, or the Bruce Springsteen concert on HBO, and looked at the file sizes, I suspect the average bit rate would be much closer to the ~14.2Mbps maximum.
 

·
Registered
Joined
·
4,039 Posts
Leszek1,


What are you using to check data rate?. I just recorded 5th Element on my Mitsu 2000 thru my Samsung T165 and it recorded in HS mode, that means data rate was over 14.1 Mbps. If I record anything between the movies from HBO HD Mitsu switches to STD mode as data rate drops below 14.1Mbps.
 

·
Registered
Joined
·
13,531 Posts
CKNA,


It sounds like he just checked the total file size, and then divided that by the total number of seconds to determine the average bit rate. If he had one of the older PC HD PVRs that recorded at 19.4Mbps regardless of channel bit rate, then he obviously used the transport->MPEG2 conversion utility.


I do find it interesting that the Mitsu switches into STD mode at
 

·
Registered
Joined
·
1,535 Posts
Discussion Starter · #9 ·
Quote:
Originally posted by CKNA
Leszek1,


What are you using to check data rate?. I just recorded 5th Element on my Mitsu 2000 thru my Samsung T165 and it recorded in HS mode, that means data rate was over 14.1 Mbps. If I record anything between the movies from HBO HD Mitsu switches to STD mode as data rate drops below 14.1Mbps.
Because instantenous rate is more than 14.1 (due to VBR), the deck will switch to HS mode. However the average rate is way below that. Dump the movie from your mitsu to your PC using DVHSTool and you will see a 10GB file.
 

·
Registered
Joined
·
1,535 Posts
Discussion Starter · #10 ·
Quote:
Originally posted by leszek1
Because instantenous rate is more than 14.1 (due to VBR), the deck will switch to HS mode. However the average rate is way below that. Dump the movie from your mitsu to your PC using DVHSTool and you will see a 10GB file.
Note: The file size from T165 will be 10GB, however it will be around 17GB from HiPix/169Time DTC100/MyHD etc. This is due to the fact that Samsung filters out null packets - others don't.
 

·
Registered
Joined
·
4,039 Posts
HD2000 adjusts its speed according to data rate. If it would drop below 14 than Mitsu would switch to STD mode. As a matter of fact, this is what happens when movie ends. HD2000 changes its speed to STD. Leszek I am not saying you are wrong, but so low data rate makes no sense for HD. We would see nothing but pixellation. Do you have Samsung T-165?.
 

·
Registered
Joined
·
3,733 Posts
""" If he had one of the older PC HD PVRs that recorded at 19.4Mbps regardless of channel bit rate, then he obviously used the transport->MPEG2 conversion utility. """


are there some of these newer cards that record at the actually bit rate, as that would allow more recording possible on a hard drive, I am very interetsd to know thanks
 

·
Registered
Joined
·
1,535 Posts
Discussion Starter · #13 ·
Quote:
Originally posted by CKNA
HD2000 adjusts its speed according to data rate. If it would drop below 14 than Mitsu would switch to STD mode. As a matter of fact, this is what happens when movie ends. HD2000 changes its speed to STD. Leszek I am not saying you are wrong, but so low data rate makes no sense for HD. We would see nothing but pixellation. Do you have Samsung T-165?.
The deck is not going to constantly switch speeds. It simply can't do that. There is a timeout for speed switch. My guess that it's around a second or so. There is plenty of data in a second - 10mbs = 1.2MB worth of stuff where the rate can peek above 14.1.


I don't own a T165, but have access to one. My copy of 5th element came from a T165
 

·
Registered
Joined
·
19,014 Posts
I just watched Kung-Pow on HBO and there was plenty of action with no pixelation/breakups of any kind. Perfectly clear.


The Tyson fight on SHO last month was terrible, lots of pixelation, virtually unwatchable.
 

·
Registered
Joined
·
2,020 Posts
Quote:
Originally posted by bfdtv
If one were to have recorded the Mike Tyson fight on Showtime, or the Bruce Springsteen concert on HBO, and looked at the file sizes, I suspect the average bit rate would be much closer to the ~14.2Mbps maximum.
Yeah but that whole Tyson fight could also fit on a floppy disk it was so short! ;)
 

·
Registered
Joined
·
3,538 Posts
Never, ever seen pixelation on HBO-HD or Sho-HD. No pixelation at all on the Tyson fight last month. My video source is from TWC using the sa3100hd box.
 

·
Banned
Joined
·
3,772 Posts
I have been using Elecard MPEG stream analyzer to study bitstreams. It is a cool tool but their datarate display seems inaccurate. For CBR recordings it shows reasonable values, but for VBR recordings of things that have repeat flags set the values seem wrong. Their old beta version showed HBO as always being some really low value like 5Mbit/sec. Their new version seems to show it as always full ATSC 19.3 even though the "null removed" file sizes doesn't show that to be true.


Various tools that analyze the bitrate have to make a choice - do we show the actual bitrate as in the stream, or do we show the "expanded" bitrate with frames repeated to the output fps?


From what I can tell, HBO, SHO, DiscoveryHD and PPV are pretty much the only things properly using repeat flags, and everything else 1080i is sending out 30fps even if was from a 24fps film source.


So - yes - I agree that HBO has a low datarate... Less than the 14.2Mbit/sec "hint" they show on their encodings.


I also think much of their content looks a bit "soft". This has led me to make the brash statement that I think they "pre-filter" everything. That would explain why they can use a very low datarate and still not show much signs of DCT/macroblocking.


As Dr1394 once said: "It all comes down to soft vs. blocky".


My library is all in HiPix full ATSC mode, and I would love to reclaim disk space by doing some sort of "null stripping", but I am afraid that I would make the files incompatible with HiPix playback.


Leszek - your TSP filter for DVHStool is a great thing, and I could use DVHStool to play back "cleaned up" recordings, but I need to consider playback on my HiPix PC. Do you have any more suggestions?
 

·
Registered
Joined
·
3,325 Posts
The whole point is that HBO and Showtime transmit their movies as 24 progressive frames each second, compared to the 30 interlaced frames each second that most local affiliates transmit. That's why they can make do with 14.2 Mbps. Things usually look very good on HBO and Showtime.


They use a variable bit-rate encoder, so the bit rate drops when there is less to encode. (e.g., a 2.35:1 letterboxed movie with black bars)
 

·
Registered
Joined
·
3,325 Posts
Quote:
Originally posted by PVR
My library is all in HiPix full ATSC mode, and I would love to reclaim disk space by doing some sort of "null stripping", but I am afraid that I would make the files incompatible with HiPix playback.
Just compress the files. PKZip, GZip, NTFS compression, tape backup compression, etc.
 

·
Registered
Joined
·
3,325 Posts
It is my opinion that HBO does not filter before encoding, but instead any differences in sharpness between movies come from the sources and/or transfer processes.
 
1 - 20 of 33 Posts
Status
Not open for further replies.
Top